Help identifying movie, underwater film from early 1980s or so...?!

Greetings;

I saw a movie on TV in the early 80s (maybe even late 70s) in which the plot was that some submariners/divers were lost and presumed dead; another sub is sent to look for them and we follow it's journey!. (These are tiny 3-man subs BTW)!. The second sub finds the trail of the first one, encountering many weird sea creatures and dangerous situations!. I don't remember too many specifics about most of the movie but I do remember distinctly at the end they find the three divers had left the first sub (it got munched somehow and they escaped in the nick of time) and were found cowering in a small rock formation in scuba gear with giant eels (I believe) circling it!. Of course, the second sub then comes to the rescue, scaring away the eels and carting the divers safely back to the surface!. Sorry this description is so vague, wish I could remember more!. Thanks in advance for ANY and all help with this one!
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